JPH02109476A - Drive method for electronic shutter - Google Patents

Abstract

PURPOSE:To improve the accuracy of exposure by providing a vertical transfer section for a pickup element, stopping high speed reversing at a specific point of time and reading a signal while a potential accepts a signal charge. CONSTITUTION:During high speed reverse transfer, the undesired charge stored in a FSPN of a CCD 1 is swept out and transferred to a vertical transfer CCD. Then the potential of the vertical transfer CCD is increased and reaches a level lower by the exposure, then a high speed reverse is stopped by a stop command. Moreover, since the readout of the signal charge to the vertical transfer CCD 1 is retarded by a prescribed time, the read signal is subject to proper exposure. Thus, the signal charge is read at a vertical transfer section without synchronization with a vertical synchronizing signal. Furthermore, when the high speed reverse transfer is stopped, the lighting of flash is stopped. Then the real time photometry is attained and a shutter with high accuracy is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving an electronic shutter used in still video cameras and the like.

[Prior Art] A so-called electronic shutter using a CCD, which is a solid-state imaging device, is generally used as a shutter for still video cameras, etc., but the driving method of the conventional electronic shutter is to transfer accumulated signal charges to a vertical transfer section. The reading is performed in synchronization with the vertical synchronizing signal of the image processing circuit (see, for example, "Television Technology", August 1987 issue, pages 37-39).

However, in order to read out the signal charge to the vertical transfer section in this way, it seems that the signal charge is synchronized with the video vertical synchronization signal.
Since the timing corresponding to the closing of the shutter is fixed, the timing of opening the shutter to obtain proper exposure is restricted by the vertical synchronization signal. For this reason, there will be variations in the time from the arbitrary timing of the release to the timing of the shutter opening, and furthermore, since the shutter opening time will be calculated based on the pre-metering data, the actual shutter opening time will vary. However, there is a limit to the improvement of photometry accuracy because the method does not measure the exposure amount of 100%, and also tends to cause variations in fog light control, especially when flash emission is required.

Additionally, a method of driving an electronic shutter in synchronization with the release switch is also known (for example, Japanese Patent Laid-Open No. 60-52
(Refer to Publication No. 1.73), no consideration has been given to the timing of opening the shutter at any time.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned conventional problems, and allows the electronic shutter to be opened and closed at any time regardless of the timing of the video vertical synchronization signal. It is an object of the present invention to provide a method for driving an electronic shutter that enables temporal photometry and improves photometry accuracy, that is, exposure accuracy.

1: Means for Solving the Problem] The present invention stops high-speed reverse transfer for sweeping out unnecessary charges from the image sensor when the exposure amount of the image sensor reaches a level lower by a predetermined amount than the appropriate exposure amount. then the same tl
This is a method of driving an electronic shutter in which signal charges are read out to a vertical transfer section after a certain period of time required for the potential of the vertical transfer section of an image element to become in a state where it can accept signal charges.

[Function] According to this driving method, high-speed reverse transfer for sweeping out unnecessary charge from the image sensor is stopped at a predetermined level below the appropriate exposure level, and it takes a certain period of time until the potential of the vertical transfer section reaches a state where it can accept charge. After waiting, the signal charges that have reached proper exposure are read out to the vertical transfer section, regardless of synchronization with the vertical synchronization signal.

[Embodiment] FIG. 1 shows the configuration of an embodiment of an electronic shutter control device for a still video camera in which the driving method of the present invention is implemented.

In the figure, the core of the electronic shutter is a CCD 1 which is an image sensor that performs photoelectric conversion, and a timing circuit 2 and V which generate drive pulses for vertical transfer and horizontal transfer to drive and control the CCD 1. It consists of a driver 3 and an H timing circuit 4.

As shown in FIG.
It has a horizontal readout CCD 1.3, a sweep drain 14, and is driven and controlled by applying a drive pulse to the vertical transfer CCD 15 of the photoelectric conversion section 11, the V transfer CCD 16 of the memory section 12, etc.

■The timing circuit 2 generates four-phase pulses φVN (hereinafter referred to as (simply called φVN)
, a pulse FSPN (hereinafter simply referred to as FSPN) for transferring the charge of the photoelectric conversion unit 11 to the vertical transfer CCD 15, and a signal EXP 1 that gives the CCD 1 the start of signal charge accumulation, that is, the timing of opening the shutter.
(hereinafter simply referred to as EXPI) and a vertical synchronizing pulse "5YNC" for φVN.

■Driver 3 connects φ to CCDI based on φVN and FSPN.
In addition, the H timing circuit 4 outputs φH that drives the horizontal readout CCD 13. EX
PI is set to rH by the ON signal from the release switch SW.
, and becomes "LJ" in synchronization with the predetermined FSPN.

The photometry unit 5 has a function to perform pre-photometry prior to exposure of the CCD 1 and a function to perform real-time photometry when the shutter is open. After switching from photometry to real-time photometry, a signal EXP2 (hereinafter simply E
XP2) is output.

As shown in the figure, this photometry section 5 includes a pre-photometry section consisting of a pre-photometering element D1, an operational amplifier 51, a resistor R, a correction voltage section 52, a switch S1, and a capacitor C1, a real-time photometering element D2, and an obe-on. 53 and capacitor C2
and a real-time photometry section consisting of a switch S2 and an operational amplifier 5.
4 and a comparator 55.

The flash control unit 6 that drives the flanche is
It operates upon receiving the signal passed through timer 7 of 1 and EXP2.

Movie 1g! The processing circuit 8 reads horizontally from the CCD1.
It receives the signal charge read from 3 and converts it into a signal for recording an image on a recording section 9 such as a magnetic disk.

The power supply unit 10 receives the ON signal of the release switch SW and supplies power to each part of the circuit.4 Next, the operation of the electronic shutter having the five configurations will be explained with reference to the time chart of FIG.

(1) When the release switch SW is turned on during the period for releasing unnecessary charges, power is supplied to each part of the circuit.
and drives CCDI.

That is, the unnecessary charge accumulated in CCD 1 is vertically transferred (': transferred to CD by FSPN, and it is swept out by φVN and transferred back to the drain at high speed. To prevent the sweeping out +10, it is removed by φVH several times. (0 times)!ll repeats. At this time, EXP 1 is "rH" and swings Sl and S2 are in the ON state.

(2) Signal charge accumulation period In synchronization with the nth FSPN, B
HJ→r l, , , transfer unnecessary charges to the vertical transfer CCD with φVN, and start accumulating the f8 charge (shimatsuta open). The unnecessary charges transferred to the stroke transfer CCD are transferred in a high-speed reverse manner and are swept out to the drain.

At this time, in order to sweep out as much as possible the smear component (unnecessary charge) generated in the vertical transfer COD, the high-speed transfer J- continues.

By the way, after that, the accumulated signal charges are transferred to the vertical transfer CC.
To read out the potential of the vertical transfer CCD to D,
It must be in a state where it can accept charges.

Now, from the stop of high-speed reverse transfer, the signal charge is vertically transferred to the CCD.
The time required to reach a state where it can be read is T (constant)
And so.

By the way, in real-time photometry with the shutter open, 'I! Even if you command the signal charge to be read out to the vertical CCD when the iJF exposure occurs, the charge will continue to accumulate for a period of time ゛, and the exposure will exceed the appropriate value by this amount. However, , if the amount of light in real-time photometry is known, the amount of exposure between T can be known.

Therefore, if a reverse transfer stop command is issued at a low level corresponding to the exposure amount during T, the signal charge will be read out to the vertical transfer CCD after 1 hour, so the read signal will be properly exposed. obtain.

At the above-mentioned timing of EXPI changing from "H" to "L", the switch Sl and $2 are turned OFF, but in the opposite state, the light amount is pre-metered by the pre-photometering element D1, and the correction voltage section 52 is turned off. A voltage lower than the appropriate level is generated by the exposure amount of time T and held in the capacitor ci, and the value immediately before the signal charge 8M starts at the timing of EXPl rH, → "L" is held.

On the other hand, when the switch S2 is opened at the same time as the signal charge accumulation starts, the real-time photometry element D2 and the capacitor C2
Real-time photometry starts.

Then, when this photometric value reaches a level that is lower by the amount of exposure during time T, the output of the comparator 54, that is, E
XP2 changes from "■1" to "L".

This "HJ-+" signal of EXP2 stops the high-speed reverse transfer, generates FSPN after a time of 1゜, and transfers the signal charge to the vertical transfer COD (shutter closed).

(3) Waiting period after high-speed transfer to memory section V transfer CO
The signal charges transferred to D are transferred at high speed to the memory section by φVN. Therefore, it waits until the vertical synchronizing signal 5YNC is input.

(4) Signal processing, after the recording period V8YNc is input, as in the conventional method,
In synchronization with the television, signal charges are read out from the horizontal readout CCD of the CCD 1 to the video processing circuit 8, subjected to signal processing, and recorded in the recording section 9.

Next, the shortest shutter speed will be explained.

EXPl becomes r I(, → "L", and unnecessary charges are transferred to the vertical transfer CCD, but all these unnecessary charges are transferred to tff
The signal charge cannot be transferred to the vertical transfer COD until it is swept out. Therefore, if the time required to sweep out only one time is Tr, then Tr+T is the shortest shutter speed. If EXP2 becomes rHJ - rL during this Tr, the shortest shutter speed is automatically set.

Next, when using the flash, the flash will be emitted with a delay of the Tr waiting time from the timing of EXPI from "H" to "L".

This means that EXP2 is r HJ −* r l during Tr
This is to prevent the occurrence of ``,'' and the flash emission was stopped at the timing when EXP2 changed from rHJ to rL.

FIG. 4 shows the configuration of the second embodiment.

This embodiment is different from the above-described one in the configuration of the photometry section 5 and the timing operation of photometry.

The photometry section 5 includes a photometry element Do, an operational amplifier 56, a voltage source E corresponding to an appropriate exposure level, and a signal EXPO'C-.
A switch SO that opens and closes to connect the voltage source E, a capacitor CO that is charged by the voltage source E, a transistor Q that discharges the charge of the capacitor CO according to the output of the operational amplifier 55, and an EXP2 that is operated by the voltage of the capacitor CO. It consists of a comparator 55 that outputs .

In the above-mentioned embodiment, the high-speed reverse transfer is stopped at the exposure level that is lower by the exposure amount corresponding to the time T than the proper exposure, but in this embodiment, the photometry is stopped before the start of charge accumulation in the CCD. The high-speed reverse transfer is started earlier by T, and is stopped when proper exposure is achieved by photometry. Even in this case, charge accumulation in the CCD starts T after the start of photometry, so when high-speed reverse transfer is stopped, there is either an underexposure corresponding to the time T or the accumulation of actual signal charges. The end is EXP2 r I-1J, r
Since it is T time later than L, proper exposure is achieved at the end of accumulation.

The operation of the photometry section 5 of the electronic shutter according to the second embodiment will be mainly explained with reference to the time chart of FIG.

(1) Unnecessary charge sweeping period When the release switch SW is turned on, Expo becomes r L J - r HJ, and the switch SO is turned on. Capacitor CO is therefore charged with a voltage source E corresponding to the proper exposure level. E by nth FSPN
Before the signal charge accumulation starts at the timing of XPl going from "H" to "L", EXPO is set to rH, → "
LJ, thereby turning off the switch SO and starting photometry.

During photometry, the capacitor CO is adjusted according to the amount of light hitting the element DO.
The charge is discharged through the transistor Q.

(2) Signal charge accumulation period nth FSPN, i.e. r of EXPO
After T time from the timing of J, EXPl is r HJ
-r L J, and signal charge starts to accumulate in CCD 1 (shutter opens).

When the capacitor CO is completely discharged, EXP2 becomes rH, rL, and high-speed reverse transfer for sweeping out unnecessary charges from CCDI by φVN is stopped.

After that, CCD 1 further charges N signal charges for T time.
(The shutter is closed to transfer the charge to the vertical transfer COD using FSPN).

The subsequent operations are the same as those described above, so the explanation will be omitted.

In addition, to explain the relationship between the exposure amount of photometric element DO and the exposure amount of CCDI in the above operation, EXPO's "HJ-+"L
” to EXPI rH,−“sh” (shutter open), only the photometric element DO is exposed and EXP
2 rH''-'rl,.

During the time T from the time FSPN (shutter closed), only the CCD 1 is exposed.

Therefore, the exposure amount at both these times must be equal, so the flash is EXPl rH'' →
It was decided to emit light between "L" and EXP2's rHJ→"L".

In each of the above embodiments, the accumulation time is controlled by the amount of light received by another photometric element during the charge accumulation of the CCD 1, but before starting the N product, the appropriate time is calculated according to the received light output. It may also be controlled by

That is, in this case, the time 2 (where Tv is the exposure time, that is, the apex value of the accumulation time) at which the proper exposure is achieved according to the light reception output of the photometering section Tv is calculated, and the time Tv is determined when 2 hours have elapsed from the accumulation time. in,
An accumulation stop signal is output.

In addition, in this case, when performing flash photography, T v starts the flash at the previous timing so that the flash completely finishes firing at the time point 2.
The reflected light from the subject due to flash emission may be received by a light receiving element different from CC and D, and when the amount of received light reaches a predetermined level, a light emission stop signal may be output.

The configuration of the photometry section according to the third embodiment is explained in the sixth embodiment.
As shown in the figure.

This photometry section includes a spot photometry section 61 that measures the subject brightness at the center of the photographic screen, a peripheral photometry section 62 that measures the subject brightness at the periphery, and a calculation section 63 to which each photometry brightness value Bvs, Bva is given. , timer ■ which is given the calculation output of the calculation unit 63 and outputs EXP2, and the calculation output and EXP
It consists of a timer (2) to which I is given, a photometry circuit section 64 for flash emission control, and the like.

This photometric circuit section 64 includes a light receiving element 65, a capacitor 66
, a switch 67, an operational amplifier 68, and six comparators. Then, the AND output of the flash enable (EN) signal from the calculation section 63 and the output of the timer 2 becomes a light emission start signal, and with this output, the switch 67
is opened and charging of the capacitor 66 is started. Further, the output of the operational amplifier 68 and the D/A conversion output from the calculation section 63 are compared by six comparison sections, and a light emission stop signal is output.

The calculation procedure by the calculation unit 63 is shown in the flowchart of FIG. 7. To explain this procedure, first, calculate α [apex value] of the central brightness value Bvs and peripheral brightness ff1B v a (#1), If α is smaller than 2, it is assumed that the object is in front light, and the processing in step #3 is performed. If α is not smaller than 2, it is assumed that the object is backlit, and processing in steps #14 and below are performed.

At the time of direct sunlight, an average value was obtained from Bvs and Bva, and this was set as Bvs #3), and Bvc + Svc - Avc was set as exposure time Tv [apex value].

Here, Svs is the sensitivity of the CCD, and Avc is the aperture value of the photographing optical system [both are apex values].

Next, compare Tv and camera shake limit time Tvh, and if the former is smaller than the latter, process #6 to #10 for low-intensity front light, and if not, perform high-brightness front light processing in #11 to #13. Process.

During low brightness front lighting, the above Tvh is set as the exposure time control value Tv.
c (#6) and turn on the flash (#7) to obtain appropriate exposure. Then, the timer I that determines EXP2 for closing the shutter has 2-TVo-T.
#8), and the timer ■ that determines the flash firing timing should be set to 2-TVc-T-Tf (just L, Tf
is the total flash emission time) (#9), and the Svc D,/A conversion output (#10) is applied to one input terminal of the comparator 69, so that the amount of light received by the light receiving element 65 is at a constant level. Stops emitting light when it reaches .

In high-brightness front lighting, based on the average photometric value obtained in #4 (
The time should be controlled by the T v value #11), the flash should not emit light #12), and the timer ■ should be set to 2-""-'T' (
t'jru (#13).

Next, when backlighting occurs, the time when the surrounding area exceeds IEv is controlled so that B v a + S v c −, A
, vc-1 is set to Tv (#14), and then a limit of camera shake limit time T v h is given to Tv (#15 to #1
7), the flash was set to emit light (#1.8), and the timer 1. ] I is the above #8. Please set it like #9.
19. #20>, Tvc + A, vcSvc - Bvs as the correction value β #21), D/A conversion output of SvC + β (
#22) is applied to the comparator 69 in the same manner as described above. As a result, the brightness Bvs of the central portion is taken into consideration, and the flash is emitted by an appropriate amount in the central portion.

[Effects of the Invention] As described above, according to the electronic shutter driving method of the present invention, high-speed reverse transfer is stopped at a level lower than the appropriate exposure amount by a predetermined amount, and the potential of the vertical transfer section is set in a state B in which signal charges are accepted. Since the signal charge is read out to the vertical transfer section after waiting a certain period of time, the signal charge accumulated up to the appropriate level in the image sensor can be read out to the vertical transfer section at any time, even if it is not synchronized with the vertical synchronization signal. can be read out,
Real-time photometry becomes possible, and a shutter with high exposure accuracy can be obtained.

In addition, the signal charge accumulation period (exposure period) is also used to sweep out unnecessary charges in the vertical transfer section. Because it is done, it can be done with low smear.

Furthermore, when using a flash, unnecessary charges are always swept away from the flash light-emitting part where smear is likely to occur, so smear can be reduced.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an electronic shutter of a video camera according to a first embodiment for carrying out the electronic shutter driving method of the present invention, and FIG. 2 is a configuration diagram showing an example of an image sensor that is the core of the shutter. FIG. 3 is a time chart J showing the operation of the first embodiment, and FIG. 4 is a configuration diagram showing the second actual fiber example.
Fig. 5 is a time chart showing the operation of the second embodiment, Fig. 6 is a configuration diagram of the photometry section in the third example, and Fig. 7 is a time chart showing the operation of the third embodiment.
It is a flowchart which shows the calculation procedure in an Example. 1... CCD (imaging device)... Vertical timing circuit, 5... Photometering section, 6... Flash control section, 1
516...Vertical conversion CCD.

Claims (2)

[Claims] (1) When the exposure amount of the image sensor reaches a level lower than the appropriate exposure amount by a predetermined amount, high-speed reverse transfer for sweeping out unnecessary charges from the image sensor is stopped, and then the vertical transfer section of the image sensor A driving method for an electronic shutter, characterized in that the signal charge is read out to a vertical transfer section after a certain period of time required for the potential to become in a state where it can accept the signal charge. (2) The method of driving an electronic shutter according to claim 1, wherein when using a flash, light emission of the flash is stopped at the time when the high-speed reverse transfer is stopped.